Embodiments of the present invention relate generally to electronic power conversion and, more particularly, to power regulation of photovoltaic (PV) arrays that provides for increased power output for such PV arrays.
Photovoltaic (PV) cells generate direct current (DC) power, with the level of DC current being dependent on solar irradiation and the level of DC voltage dependent on temperature. When alternating current (AC) power is desired, an inverter is used to convert the DC energy into AC energy, such as AC energy suitable for transfer to a power grid. Typical PV inverters employ two stages for power processing. The first stage of the PV inverter is configured to regulate a widely varying DC voltage from an array of PV cells, so as to provide a constant DC voltage output. The second stage of the PV inverter is configured to convert the constant DC voltage to AC voltage. Often, the first stage includes a boost converter, and the second stage includes a single-phase or three-phase inverter system.
One common arrangement in PV systems is for several PV modules to be connected in series to form a PV string, with multiple PV strings in a PV system then being connected in parallel to supply more current. In PV systems where a great number of PV strings are connected in parallel, it is required that all string voltages be identical based on their parallel connection. However, the optimal operation voltage of each PV string might not be the same in terms of maximum power extraction. That is, due to shading issues, uneven temperature distribution, and/or other specific characteristics of individual PV strings, the optimal voltages for each PV string may vary. While the differences in the optimal operation voltages for each PV string are typically small (i.e., less than 20V), the parallel connection of PV strings can still lower the efficiency and production of the PV system up to about 15%.
It would therefore be desirable to provide a PV system that functions to operate each PV string at its optimal voltage so as to achieve maximum power extraction. It would also be desirable to provide a PV system that is able to track voltage and power outputs for each PV string and implement a technique for dynamically controlling each PV string.